Large bodies capable of uniformly generating and emitting light across an extended two-dimensional surface, for example, light-emitting foils which can be used in panel or back lighting systems, are presently unavailable. However, light guides are common elements in contemporary display and lighting technology. In combination with a plurality of suitably placed light-extracting elements light guides can be utilized to implement large sized panels which can generate uniform lighting impressions. Such a system can redirect light emitted from one-dimensional extended tubular or point light sources positioned along the edge of the panel such as described in International Patent Application Publications WO 03/083564 and WO 03/083562. These patent applications disclose thin back lighting systems based on edge lighting of acrylic sheets with front-emitting light-emitting diodes along the periphery and a machined light extracting pattern on a surface of the acrylic sheet.
As previously defined, edge lighting utilizes substantially one-dimensional light sources positioned along the periphery of the panel or rows of point light sources. Edge lighting is widely used in back lit displays and screens with screen sizes of up to approximately half a meter measured along the diagonal. However, edge lighting limits the maximum panel size which can be uniformly illuminated because of light attenuation and aberration due to optical effects inside and at the edge of the panel or light guide. For various reasons, these effects cannot be compensated by providing increased amounts of light at the edge of the light guide to build substantially arbitrarily large panels. Furthermore, the placement of light-extracting elements needs to be customized for the size of the panel which economically impedes arbitrary panel size scaling.
The scale-up limitation in large screen display technology has been addressed and a solution was published summarizing the state of the art in “LED Backlighting from Revolution to Reality” at “The 6th Annual Display Search US FPD Conference” held between Mar. 30 and Apr. 1, 2004. It describes a system comprising a number of side light-emitting diodes which are located inside holes in a two-dimensional extended light guide instead of positioned along one or more edges of the light guide. The system utilizes a sophisticated combination of diffusive optical elements which can achieve uniform screen back lighting.
The state of the art in display systems however, does not provide technological or economic solutions for architectural lighting, for which large surfaces need to be illuminated. Therefore there is a need for a new lighting system which can solve the problems identified in the current state of the art.
This background information is provided to reveal information believed by the applicant to be of possible relevance to the present invention. No admission is necessarily intended, nor should be construed, that any of the preceding information constitutes prior art against the present invention.